The invention relates to an automatic clutch controls system which automatically control the coupling of a driven shaft to a drive shaft in a clutch mounted on an automobile in accordance with a decision rendered by an electronic unit.
In a conventional automatic clutch arrangement, the degree of engagement of the clutch is determined in an analog manner in accordance with the number of revolutions of an engine only upon starting, but an on-and-off control of the clutch is employed during a subsequent shift operation which occurs after the vehicle has been started. Consequently, if there is a difference between the number of revolutions of the engine and the number of revolutions of the clutch to cause a sudden complete engagement of the clutch, a driver of the vehicle may experience an uncomfortable shock. To alleviate this, a variable rate is employed for engagement of the clutch, since the magnitude of a negative pressure prevailing in an engine manifold allows the differential number of revolutions to be known. However, the technique suffers from a disadvantage that an accurate control cannot be achieved since the magnitude of the negative pressure changes from vehicle to vehicle and because a long time delay is involved.
To accomodate for this difficulty, an arrangement has been proposed to achieve an accurate engagement of a clutch without experiencing a shock in a clutch arrangement in which a clutch transmits rotating power to an output shaft. The arrangement comprises a power sensor for detecting the number of revolutions of the output shaft, a clutch sensor for detecting the number of revolutions of the clutch, a comparator for determining the relative magnitude of the number of revolutions of both sensors, a parameter of follow-up control responsive to an output from the comparator to activate the clutch for engagement as the number of revolutions of the output shaft increases whenever the number of revolutions of the output shaft is higher than that of the clutch, and an automatic engaging circuit responsive to an output from the comparator and operating whenever the number of revolutions of the clutch is higher to deactuate the follow-up control and to terminate automatically the engagement of the clutch within a given time interval. In this manner, the relative magnitude of the number of revolutions of the engine and the clutch is determined in an electrical manner, and whenever the number of revolutions of the engine is higher than that of the clutch, an engagement of the clutch occurs in response to the number of revolutions of the engine while whenever the number of revolutions of the engine is lower than that of the clutch, an engagement of the clutch takes place in accordance with a difference therebetween. (See Japanese Patent Publication No. 26,020/1978, filed Mar. 26, 1971 and published July 31, 1978). In other words, the rotational speed of the engine is chosen as a main variable while a differential speed between the output shaft of the clutch (driven shaft) and the output shaft of the engine (the clutch drive shaft) is chosen as a parameter for controlling the clutch coupling power. To summarize, in a mode in which the vehicle is driven for running under the engine power, the clutch coupling power is controlled in a manner corresponding to the rotational speed of the engine while in an engine brake mode, the clutch coupling power is controlled as a particular function of time. Consequently, the slip rate of the clutch depends on the rotational speed of the engine, and the correlation between the engine power and a load on the vehicle may not be proper. To achieve a proper engagement of a clutch for various running conditions of a vehicle, it is preferred that the slip rate of the clutch correspond to the running condition of the vehicle.
In either instance of conventional arrangements in which the degree of engagement of the clutch is determined in accordance with the number of revolutions of the engine upon starting the automobile or in which the clutch coupling force is controlled in accordance with the rotational speed of the engine with a speed differential between the input and the output shaft of the clutch acting as a parameter, it will be seen that the rotational speed of the engine will exhibit a change corresponding to a loading on the automobile and the engine power after the clutch engaging force has exceeded a given value, so that it can be concluded that a control over the engagement of the clutch takes place in a manner corresponding to the loading on the vehicle and the engine power. However, at the initiation of coupling of the clutch upon starting the vehicle and immediately thereafter, namely, until a degree of coupling force is established, the occurrence of shocks is unavoidable to a degree. By way of example, if a throttle is smoothly opened from its idling position when a shaft lever is placed in the drive or reverse position, the coupling force of the clutch increases from its off condition corresponding to the idling condition in a smooth manner with an increase in the rotational speed of the engine. However, above a throttle opening which corresponds to the idling condition, or in other words, when the rotational speed of the engine exceeds an idling speed, a change of the shift lever position to the drive or reverse position establishes a relatively high value of coupling force of the clutch independently from the loading on the vehicle (road condition) to thereby cause the occurrence of starting shocks, which result in a rapid reduction in the rotational speed of the engine and a rapid reduction in the coupling force of the clutch as transients.